The present invention relates to hearing aid systems, and more particularly to a hybrid hearing aid system that combines a cochlear stimulator and a hearing aid to provide a hearing aid system that relies primarily on the cochlear stimulator portion of the system for being able to sense high frequency sounds, and that relies primarily on normal hearing processes, or a hearing aid, for being able to sense lower frequency sounds. Such hybrid hearing aid system is best suited for use with a short cochlear electrode array of the type described in applicant""s copending patent application, filed concurrently herewith, entitled xe2x80x9cElectrode Array for Hybrid Cochlear Stimulatorxe2x80x9d (Attorney Docket Number AB-084-PC), which application is incorporated herein by reference.
A hybrid cochlear stimulation system provides electrical stimulation only to the basal end of the cochlea to stimulate ganglion cells responsible for sensing higher-frequency sounds, and relies on normal hearing (activation of hair cells through fluid motion within the cochlea), which may occur with or without the assistance of a conventional or a custom hearing aid, to sense middle-to-lower frequency sounds.
Hearing loss is generally of two types: conductive and sensorineural. Of these, conductive hearing loss occurs where the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss may often be helped by use of conventional hearing aids, which amplify sound so that acoustic information does reach the cochlea and the hair cells. Some types of conductive hearing loss are also amenable to alleviation by surgical procedures.
Sensorineural hearing loss, on the other hand, results due to the absence or the destruction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. Persons who suffer from sensorineural hearing loss are unable to derive any benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because their mechanisms for transducing sound energy into auditory nerve impulses have been damaged. Thus, in the absence of properly functioning hair cells, there is no way auditory nerve impulses can be generated directly from sounds.
To overcome sensorineural deafliess, there have been developed numerous cochlear implant systemsxe2x80x94or cochlear prosthesisxe2x80x94which seek to bypass the hair cells in the cochlea by presenting electrical stimuli directly to the ganglia of the auditory nerve located adjacent the modiolar wall of the cochlea. When triggered, the ganglia, also referred to as ganglion cells send nerve impulses to the brain via the auditory nerve, leading to the perception of sound in the brain, and an at least partial restoration of hearing function. The common denominator in these cochlear prosthesis systems has been the implantation into the cochlea of electrodes which are responsive to a suitable external source of electrical stimuli and which are intended to transmit those stimuli to the ganglion cells, and thereby to the auditory nerve fibers.
As people age, they frequently experience progressive hearing loss. Usually this loss is more prevalent and more sever at higher frequencies. Thus, it is estimated that a large segment of the hearing-impaired population exhibit sensorineural hearing loss relative to high frequency sounds, but maintain the ability to transduce middle-to-lower frequency sounds through functioning hair cells.
The usual method to restore this high frequency hearing loss is by using a hearing aid that increases the amplitude of the acoustic energy applied to the tympani membrane. Although effective, this approach does not provide the same level of restoration to high frequencies as it does to lower frequencies. Also, the increase in acoustic amplitudes used in this method can ofttimes further degrade residual hearing, resulting in a further decrease in the ability to hear the higher frequencies.
It is thus evident that there is thus a need for a xe2x80x9chybridxe2x80x9d cochlear stimulation system that electrically stimulates only the ganglion cells responsible for sensing higher frequency sounds, while allowing or permitting the normal hearing process (e.g., activation of hair cells through wave motion of the fluid within the cochlea) to function for the purpose of sensing lower-to-middle frequency sounds.
A cochlear prosthesis operates by direct electrical stimulation of the auditory nerve cells, bypassing the defective cochlear hair cells that normally transduce acoustic energy into electrical activity in such nerve cells. Because the ganglion cells responsible for sensing higher frequency sounds are all generally located in or near the basal end of the cochlea (the end of the cochlea nearest the basal membrane), a hybrid cochlear stimulation system thus requires an electrode array that can be inserted within the cochlea a sufficient depth to be near such cells, but which also does not block or significantly interfere with the normal functioning of the cochlea for hair cells located deeper within the cochlea. Thus, there is a need for such an electrode array that may be used with a hybrid implantable cochlear stimulator hearing aid system.
The present invention addresses the above and other needs by providing a hybrid implantable cochlear stimulator and hearing aid system that relies primarily on the cochlear stimulator portion of the system for being able to sense high frequency sounds, and that relies primarily on normal hearing processes, or other acoustic boosting devices and systems, for being able to sense lower frequency sounds. Such hybrid hearing aid system uses a relatively short and unobtrusive cochlear electrode array, e.g., of 6-8 nun in length, of the type described in applicant""s copending patent application, previously referenced, entitled xe2x80x9cElectrode Array for Hybrid Cochlear Stimulatorxe2x80x9d (Attorney Docket Number AB-084-PC), or something equivalent thereto.
A hybrid cochlear implant hearing aid system in accordance with the present invention provides low frequency acoustic energy boost, if needed, and high frequency direct neural stimulation. The high frequency neurons are located at the basal end of the cochlea, providing easy access for the surgical placement of a short electrode that stimulates only the high frequencies. The electrode array typically has from four to eight electrode contacts, e.g., 4 or 5 electrode contacts. The design of the electrode array allows the surgeon to place the array using minimally invasive surgical techniques and requires no cochleostomy. The electrode array is thin, and can typically be inserted directly through the round window membrane to make contact with, or to be positioned in close proximity to, the modiolus wall in the basal region of the cochlea.
The front-end amplifier and processor and spectral decomposition filters used with the hybrid system of the present invention may be the same for both acoustic boost and neural stimulation applications. The frequencies are separated and sent to circuits that either convert them into mechanical vibrations to boost low-to-middle frequency acoustic energy, or into high frequency energy that is further divided and converted to stimulation pulses that are applied directly to the neurons located in the basal region of the cochlea through the short electrode. A smoothing circuit may be provided to allow a smooth, seamless transition from the acoustic enhancement provided for low-to-middle frequencies and the neural stimulation provided for the high frequencies.
In accordance with one aspect of the invention, tinnitus (which is a buzzing, or ringing, sound in the ear) is suppressed by delivering special pulse sequences on some of the electrodes located in the basal region of the cochlea, while acoustic enhancement is provided in the low frequency range.
Advantageously, the hybrid system of the present invention may be used for several applications. Such applications include, but are not limited to:
(a) high frequency neural stimulation combined with residual low frequency hearing;
(b) high frequency neural stimulation signal enhancement combined with low frequency acoustic signal enhancement;
(c) tinnitus suppression;
(d) tinnitus suppression combined with acoustic signal enhancement;
(e) high frequency neural stimulation signal enhancement, acoustic signal enhancement, and tinnitus suppression stimulation; or
(f) tinnitus suppression combined with cochlear neural stimulation.
It is thus a feature of the present invention to provide a hybrid cochlear stimulation and hearing aid system that restores hearing function over a wide frequency band, e.g., from low frequencies to high frequencies.
It is a further feature of the invention to provide such a hybrid system wherein minimally invasive surgical techniques are employed.